This invention relates generally to the field of electrostatography, and more particularly, the invention relates to a method and apparatus for fixing toner images to a support by means of heat and pressure.
In an electrostatographic process, an image formed by fusible toner particles is transferred to a support such as a copy sheet. The toner image is permanently fixed to the support by passing the support through a fuser. In one such fuser, the support is passed between a pair of opposed rollers, one roller being a heated fuser roller and the other roller being a non-heated pressure roller.
Fused toner images normally exhibit a dull or matte surface. In certain types of images, particularly colored toner images, it is desirable for the image to have a surface gloss. One example of apparatus for fusing colored images is shown in U.S. Pat. No. 4,223,203. In this patent, there is disclosed fusing apparatus for fixing toner images to copy substrates comprising a first pair of rolls, one of which is provided with a conformable outer surface, and a second pair of rolls, one of which has a rigid outer surface. Copy sheets are passed sequentially through the first and second pairs of rolls, the first pair serving as a fuser means and the second pair as a glossing means. There is a problem in using such apparatus under certain operating conditions, for example, when coated paper is used, in that the prints tend to show blistering and curling after the fusing process.